The Effect Of Ferrihydrite On Methane Emission From Paddy Of Oryza Rufipogon Griff.and Microbial Community Structure

Methane is the second greenhouse gas after carbon dioxide.And as the main anthropogenic sources,the methane emission from rice has reached 9%of total methane in the atmosphere.While the wild rice O.rufipogon has rich genetic diversity and is the valuable genetic resources in rice cultivar breeding.And the root iron plaque formed after applying ferrihydrite to rice field is beneficial to decrease methane emission.So taking advantage of ferrihydrite and wild rice will put forward a new solution about methane emission reduction and relieving the contradiction between global greenhouse effect and grain production.In my thesis,Oryza rufipogon were the main materials and the needed populations were selected through iron stress.Then according to the pot and plot planting,the experiment adopted the method about biogeochemistry,such as measuring the root porosity by pycnometer method,extraction of iron plaque on roots by DCB,measuring the iron concentration by atomic absorption spectrophotometer,measuring methane emission by closed static chamber technique,measuring methane concentration by GC gas chromatograph,measuring methane production potential by thermostatic anaerobic culture,measuring Fe(Ⅱ)and Fe(Ⅲ)concentration by spectrophotometric method of ferrozine,and the method about molecular microbial ecology,such as PCR,terminal-restriction fragment length polymorphism and real-time quantitative PCR detecting system to research the effects of ferrihydrite on methane emission from wild rice and microbial community structure.The research results were as follows.(1)Eight different Oryza rufipogon from different areas in Hainan province had different situations on the biological characteristics,root porosity,roots surface area and iron plaque on roots.Especially it had extremely big difference on roots,including XLB、FLV and MXV populations which had big biomass between 300 g and 500 g,and HLY、HGV、HQF、YYY and MBV populations which had small biomass between 100g and 300g.According to the iron plaque indexes,we can know that the population which had the strongest forcing ability of iron plaque was HLY populations which its content of iron plaque on roots was 22.25 mg Fe/g dry root,amount of iron plaque on roots of a plant was 6.04 mg Fe/a plant,thickness of iron plaque on roots was 0.0196 mg Fe/cm2 and standard iron plaque on roots was495.70 mg Fe/cm,and they were all extremely significantly(P<0.01)or significantly(P<0.05)higher than MBV populations which had the weakest forcing ability of iron plaque and its four iron plaque indexes were 7.96 mg Fe/g dry root,0.97 mg Fe/a plant,0.0070 mg Fe/cm2 and 68.12 mg Fe/cm respectively.The amount of iron plaque on roots of a plant had extremely significantly(P<0.01)positive correlation with the taproot surface area,lateral root surface area,total root surface area and total bulk of a plant,so if the roots surface area was used to reflect the formation ability of iron plaque,the index of amount of iron plaque on roots of a plant was the best.The standard iron plaque on roots had extremely significantly(P<0.01)positive correlation with the lateral root surface area per gram dry root and lateral root surface area of a plant,so if the lateral roots surface area was used to reflect the formation ability of iron plaque,the index of standard iron plaque on roots was the best.In this experiment it was also found that the highest content of iron plaque on roots were HLY and HQF populations which had moderate root biomass,and the content were 271.67 g and 205.00 g respectively.Then their thickness of iron plaque on roots and standard iron plaque on roots were higher accordingly.But the lowest content of iron plaque on roots were FLV and MBV populations that their biomass were in two extreme,and the content were 466.33 g and 121.33 g respectively.While their thickness of iron plaque on roots and standard iron plaque on roots were lower accordingly.So moderate growth of roots may be beneficial to the formation of iron plaque.(2)In the pot experiment of the wild rice HLY population with thick iron plaque and the wild rice MBV population with thin iron plaque,both of them showed that methane emission flux,methane concentration and Fe(II)concentration in pore water of soil had cut down after applying ferrihydrite.As well as,the reduction of methane emission of HLY population was 6.61%and less than 16.24%of MBV population.However,the methane emission flux,methane concentration and Fe(II)concentration in pore water of soil of HLY population was less than MBV population.The inhibiting effects of iron plaque on methane production mainly were reflected in earlier stage of two populations and later stage of MBV population.In earlier stage,the group of MBV populations with Fe inhibited the methane production because of higher amount of iron plaque on roots of a plant,but the control group of HLY populations had less methane emission than the group with Fe on account of higher amount of iron plaque on roots of a plant.In later stage of MBV populations the group with Fe had less root biomass but more methane concentration in soil pore water.Because the group with Fe had less amount of iron plaque on roots of a plant than the control group and its inhibition effects was not better than the the control group,and finally produced more methane.Both populations indicated that the content of iron plaque on roots,Fe(Ⅱ)and Fe(Ⅲ)concentration in soil had increased after applying ferrihydrite.Fe(Ⅲ)was the main form in rhizosphere soil and bulk soil,also Fe(Ⅱ)and Fe(Ⅲ)were higher in rhizosphere soil than in bulk soil.It had inhibiting effects on methane production rate of soil and rice roots cultured in an anaerobic environment after applying ferrihydrite.Even the methane production rate of rice roots of the group with Fe were all extremely significantly(P<0.01)less than the control group.(3)In the plot experiment of the wild rice HLY population with thick iron plaque and the rice BIY 26 with thick iron plaque,applying ferrihydrite had no reduction of methane emission on rice or wild rice.And that the methane emission flux of wild rice was greater than rice but methane concentration and Fe(Ⅱ)concentration in pore water was less than rice.Meanwhile,the methane concentration and Fe(Ⅱ)concentration in pore water of wild rice had decreased after applying ferrihydrite.The inhibiting effects of iron plaque on methane production mainly were very obvious in rice and wild rice.In 50～51 d,the root biomass of rice group with Fe was less than the control group.But its amount of iron plaque on roots of a plant was less than the control group,which led to produce more methane.The root biomass of wild rice group with Fe was more than the control group and amount of iron plaque on roots of a plant was less than the control group,so the methane concentration in pore water was more than the control group.In 89～90 d,the root biomass of the control group was more than rice group with Fe.But its amount of iron plaque on roots of a plant was significantly(P<0.05)more than rice group with Fe,which had more inhibition effects on methane production and led to produce less methane.The root biomass of wild rice group with Fe was more than the control group and amount of iron plaque on roots of a plant was more than the control group,so the methane production was less than the control group.The biological characteristics of wild rice were superior to rice.For rice and wild rice,their iron plaque on roots both had decreased but Fe(Ⅱ)and Fe(Ⅲ)concentration in soil had increased after applying ferrihydrite,and also had different effects on methane production rate of soil and roots cultured in an anaerobic environment.(4)The experiment in pot and plot had the same conclusion on microbial community structure.The dominant archaea communities of soil and roots were Methanocellales and Methanosaetaceae.The second were hydrogenotrophic Methanobacteriaceae which were more in roots and acetotrophic Methanosarcinaceae which were more in soil.No matter in bulk soil,rhizosphere soil or roots,the hydrogenotrophic methanogens was more than acetotrophic methanogens and were twice as much as acetotrophic methanogens in roots.The quantity of methanogens and Geobacter bacteria in rhizosphere soil both were more than bulk soil.In the earlier stage of pot experiment and two stage of plot experiment,bulk soil and rhizosphere soil both showed up that the treatment with more methanogens had more Geobacter because of the syntrophic growth relationship.